A reverse osmosis membrane is a very tightly wrapped microfiber that has a .001 micron rating. Water is forced through the RO membrane by water pressure. Only the purest water molecule can penetrate the RO membrane. The water that permeates the RO membrane is called dilute SOLUTION, permeate, product or pure water. the Rest of the water and impurities are flushed away down the drain LINE. This waste water is called BRINE, concentrate or waste water.